The acquisition of sterol by the fetus is essential for development and growth. The fetus has two potential sources of cholesterol, de novo synthesis and exogenous sterol. Without the required amount of cholesterol from these sources, the fetus will not survive or will develop abnormally. Data obtained during our previous funding period suggests that the fetus acquires cholesterol from the maternal circulation in addition to that derived from de novo synthesis. The accretion of maternal- derived sterol seems to be dependent upon the sterol balance in the extra-embryonic fetal tissues that protect the fetus from direct contact with circulating maternal constituents, the placenta and yolk sac. Thus, the hypotheses for the present proposal are 1) that the fetus acquires cholesterol from the maternal circulation and 2) that the maternal cholesterol within the fetus is metabolically active. There are 4 specific aims which will test these hypotheses. First, the amount of cholesterol acquired from the maternal circulation will be quantitated. To delineate the processes involved, transport will be examined using different lipoproteins at different stages of development and with varied maternal plasma cholesterol concentrations. The role of specific proteins that have been implicated in fetal development will also be examined in genetically altered animals lacking the proteins in question, such as megalin. Second, the processes involved in the uptake, transport and secretion of cholesterol from the placenta will be evaluated. These studies will be completed in a human derived carcinoma trophoblastic cell line and in human placental perfusions. To examine the processes, we will study the effects of increasing concentrations of lipoproteins (LDL and HDL), cellular cholesterol and lipid acceptors (lipid-poor apoAI and phospholipid vesicles). Third, the effectors of lipoprotein secretion from the yolk sac will be determined in a yolk sac organ culture. Cholesterol and triglyceride concentrations and triglyceride composition will be manipulated in the yolk sacs and the resultant effect this has on lipoprotein secretion will be examined. The role of specific proteins in this process will also be examined. Finally, the processing of proteins involved in sterol balance, the sterol regulatory element binding proteins, and the activation of Sonic hedgehog, a protein involved in patterning of the forebrain, will be studied in fetal tissues that have accrued different amounts of maternal cholesterol. Based on the results of this proposal, we expect to define new approaches to enhance the presentation of exogenous cholesterol to the developing fetus or embryo.